What mysteries of Star Trek would you like to see solved (and, if you want to say it, how would you solve them)?

Ther are many things in Star Trek that are not explained. Origin of Borg. Who the Jem;Hadar were before the Founders modified them. What is the origin of Q. Barash's species. Where did all these strtange entities from TOS came from It woul take a lot to list all of it. I ask you: what star Trek mystery would you liek to see solved. And, if you want, tell is how would you solve it (in as many details, or as less, as you want).